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Salty Ceres

April 11, 2016

If explorers of the future ever get tired, aching feet from walking around on Ceres, they won’t have far to go for some relief. Deposits of Epsom salts seem to be sprinkled across much of the surface, forming bright white spots.

The spots were discovered by Dawn, a spacecraft that’s been orbiting Ceres for the last year. The craft saw the brightest of them when it was still tens of thousands of miles away from Ceres. There was much speculation about the nature of these spots — from deposits of pure ice to the lights of alien bases.

Ceres is the largest body in the asteroid belt between the orbits of Mars and Jupiter. Its surface is rugged and bumpy, with several large impact craters. One of those contains the bright spots that created all the excitement. Known as Occator, it’s about 60 miles wide and a mile deep. And it’s quite young — less than 80 million years old.

Most of the other white spots on Ceres are also associated with craters. That suggests that the material in the spots came from a layer below the surface. The impacts drilled down to that layer, exposing some of the deeper material.

A study published last year said the material is probably a brine — a mixture of ice and magnesium sulfate — the same mineral found in Epsom salts. Ceres has no atmosphere, so once this mixture is exposed to space, the water vaporizes. In fact, some water vapor is still escaping from the crater today — leaving bright white deposits across its floor.


Script by Damond Benningfield

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